The present invention relates to a thermally sensitive recording medium whose preservability, printability and glossiness are improved.
Generally, a thermally sensitive recording medium having a thermally sensitive layer mainly composed by colorless or pale colored dye precursor which is an electron donating dye precursor (hereinafter shortened to a dye precursor) and a color developer which develops color by a chemical reaction with the dye precursor when heated, is disclosed in Japanese Patent Publication 45-14035 and is widely and practically used. For a recording means of a thermally sensitive recording medium, a thermal printer in which a thermal head is built in is used. This recording method is superior to the conventional ordinary recording methods from the view points of noiseless recording, no need of development and fixing procedures, maintenance free, relatively cheap and compact and very clear image. Therefore, this procedure is widely used in the fields of facsimile and computer, various kinds of measuring equipment and labels.
However, in a case of a conventional thermal recording medium, since only a thermally sensitive recording layer whose main components are dye precursor, color developer and fixing agent is coated on the surface of substrate, the resistances against light, water, heat, plasicizer and oil are not stable and the color change by aging at preservation is pointed out as a problem. Further, in a case of this type of thermal recording medium, the glossiness of image part and non-image part is not considered.
To solve the problem of the conventional thermally sensitive recording medium, a method of forming a protecting layer over the surface of thermally sensitive recording layer has been suggested. For example, the method to use hydrophobic emulsion of high polymer compound is disclosed in Japanese patent Laid Open Publication 56-146794 or the method to form an intermediate layer of water soluble high polymer compound or hydrophobic emulsion of high polymer compound and then to form a surface layer by oil type coating composed by hydrophobic high polymer compound over above mentioned intermediate layer is disclosed in Japanese Patent Laid Open Publication 58-199189. In these methods, the preservative property of the image is improved, however, the glossiness is very low.
In general, UV varnish is coated over the surface of the thermally sensitive recording medium to provide the lustrous property, however, this method has several problems. That is, since the thermally sensitive recording medium by this method generates stickiness during the printing procedure, it is not suited to use with a thermal head. Further, the fixing of ink on this thermally sensitive recording medium is not good and the printing property of it is not sufficient. In Japanese Patent Laid Open Publication 1-178486, the thermally sensitive recording medium having an intermediate layer composed by water soluble high polymer, pigment and cross-linking agent on the thermally sensitive recording layer, further having a glossing layer composed by lustrous hydrophobic high polymer compound and a slipping agent on the intermediate layer is described. However, since this glossing layer is coated using solvent, the working efficiency for coating is very bad and is not sufficient for practical use.
Further, in Japanese Patent Laid Open Publication 2-169292, the thermally sensitive recording medium on which a protecting layer mainly composed by wax, resin, inorganic pigment smaller than 0.5 xcexcm average diameter or composed mainly by resin and inorganic pigment smaller than 0.5 xcexcm average diameter is disclosed. And, in Japanese Patent Laid Open Publication 2-175281, the lustrous thermally sensitive recording medium which has protecting layer composed by silica whose average diameter is smaller than 0.05 xcexcm and/or calcium carbonate and water soluble binder is disclosed. If any of these protecting layers is formed, and printed by a thermal head, glossiness of the surface is deteriorated and sometimes a problem of sticking is generated. Further, in Japanese Patent Laid Open Publication 1-122483, the thermally sensitive recording medium which forms a protecting layer on the thermally sensitive recording layer mainly composed of water soluble resin formed on a substrate, and whose surface glossiness based on JIS-P-8142 is bigger than 40(GS(75xc2x0))% is described. However, when this thermally sensitive recording medium is printed by thermal head, sometimes there is a problem that the glossiness is hurt.
The object of the present invention is to solve above mentioned problems and to provide a thermally sensitive recording medium whose suitability for a thermal head and suitability for printing is improved.
The inventors of this invention, have conducted an intensive study and have found that a thermally sensitive recording medium which has good image preserving ability and glossiness can be obtained by forming a glossing layer mainly composed by an inorganic pigment and a fixing composition having heatproof sticking tendency which does not cause sticking at higher temperature on a thermally sensitive recording layer formed on the substrate, and accomplished the present invention.
That is, a thermally sensitive recording medium of this invention is characterized by forming a glossiness layer containing mainly an inorganic pigment and a fixing composition which does not cause sticking at higher temperature than 200xc2x0 C. on the thermally sensitive recording medium formed on a substrate, and the surface glossiness based on JIS-P-8142 (an angle of incidence and an angle of reflection is 75xc2x0) of the glossiness layer is higher than 50%. If more improved image preservative ability and glossiness are required, it is effective to form an intermediate layer between the thermally sensitive recording layer and a glossiness layer composed mainly by inorganic pigment and fixing composition.
In the present invention, as the example of an inorganic pigment used in the glossiness layer or in the intermediate layer, the compound which does not hurt the property as the thermally sensitive recording medium and glossiness can be used. As the concrete example, metal oxide such as silica, colloidal silica, titania, zirconia, alumina, antimony pentaoxide or zinc oxide, metal carbonate such as calcium carbonate or magnesium carbonate, aluminum hydroxide and barium sulfate can be mentioned, however, it is not intended to be limited to these pigments. These compounds can be used singly or in combination. Especially among these compounds, colloidal silica and barium sulfate are very useful to obtain an excellent lustrous surface because the primary particles of these compounds are stable and do not form flocks, further the refractive index of these particles is comparatively low. And, the dispersion of colloidal silica and barium sulfate is very stable and hardly forms a precipitate, further since fine particles of these compounds can be dispersed in comparatively high concentration, the coating amount can be adjusted to higher level and has high work efficiency. Therefore, these compounds are desirably used.
In this invention the property of fixing composition which does not cause sticking at higher temperature than 200xc2x0 C. is measured by following method.
(1) On paper of 60g/m2 density and 74 xcexcm thickness, the fixing composition is coated by 20 g/m2, left for 5 minutes in an oven of 110xc2x0 C. and the coated layer of fixing composition is completely hardened.
(2) The obtained coated paper is cut to 4 cmxc3x978 cm size and doubled up so that the coated surface with fixing composition is contacted. Thus the specimen of 4 cmxc3x974 cm size is prepared.
(3) The specimen is placed on a hot plate heated to 200xc2x0 C. and a weight of 500 g (whose base diameter is 4 cm) is placed on the specimen for 5 seconds. Then the specimen is cooled down to room temperature, and checked whether the contacted coated surfaces can be separated easily or not.
In this invention, the fixing composition which does not cause sticking at higher temperature than 200xc2x0 C. is prescribed as follows. Namely, the specimen whose contacted coated surfaces does not cause sticking, that is, the coated surface does not become sticky and can be separated easily, or causes partial sticking, but can be easily removed, are ranked as the fixing composition which does not cause sticking at higher temperature than 200xc2x0 C.
In the conventional thermally sensitive recording medium which has lustrous property, the generation of following problems is pointed out. Namely, at the printing procedure, the glossiness is spoiled, striped lines and cracks appear and the printed image becomes blurred. The cause of these problems is the destruction of a glossing layer (or a protecting layer) by instantaneous heating at 200-300xc2x0 C. of a thermal head. Namely, a binder component in the glossing layer becomes sticky by instantaneous heating and adheres to the thermal head, and since a recording paper is fed through the soiled thermal head, the glossing layer is partially removed. On the contrary, the thermally sensitive recording medium of this invention is an improved one whose heat resistance for destruction is improved by use of a fixing composition which does not cause sticking at higher temperature than 200xc2x0 C. That is, the glossing layer of this invention does not generate sticking property even if exposed to high temperature, and the removing of glossing layer can be effectively prevented.
As the fixing composition used in the glossing layer of this invention, any composition which does not cause sticking at the higher temperature than 200xc2x0 C. and does not hurt the thermal sensitivity and lustrous property can be used. Concretely, various kinds of polyvinyl alcohol of 200xcx9c2500 polymerization degree such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, denatured polyvinyl alcohol e.g. polyvinyl alcohol denatured by carboxyl, polyvinyl alcohol denatured by amide, polyvinyl alcohol denatured by sulfonic acid or polyvinyl alcohol denatured by butylal (butyl aldehyde); water soluble high polymer of cellusose derivatives, such as, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and acetyl cellulose and (meth)acrylic ester resin such as (meth)acrylic ester copolymer, acrylic ester and/or methacrylic ester, copolymer of styrene and/or vinyl acetate, copolymer of acrylamide/acrylic ester/methacrylic acid, copolymer of colloidal silica complex acrylic ester and copolymer of colloidal silica complex styrene/acrylic ester can be mentioned. However, it is not intended to be limited to them.
Among above mentioned water soluble high polymer substances, a highly saponified polyvinyl alcohol has an excellent resistance to sticking by heat, its use is preferred. Especially, the water soluble high polymer substance whose degree of saponification is bigger than 90% and degree of polymerization is bigger than 1000 is preferably used. As concrete examples of these, xe2x80x9cPVA-117xe2x80x9d (degree of saponification:98.5, degree of polymerization:1700) of KURARAY Co., Ltd. can be mentioned.
In this invention, the property of not causing sticking at the temperature higher than 200xc2x0 C., is most important, and in comparison with the thermally sensitive recording medium containing the fixing composition which causes sticking at the temperature lower than 200xc2x0 C., the improvement of the resistance to sticking by heat of the glossiness layer is remarkable. Even if the fixing composition does not display good resistance to sticking by heat at the temperature higher than 200xc2x0 C., when used alone, if it displays good resistance to sticking by heat by use together with an additive, such as, cross-linking agent, it can be used as the fixing composition which does not cause sticking at the higher temperature than 200xc2x0. That is, the fixing compound of this invention is a compound which display fixing ability by single use of the compound or as a composition containing additives.
As the acrylic ester type resin, colloidal silica complex acrylic ester copolymer disclosed in Japanese Patent Laid Open Publication 7-26165, or (meth) acrylic ester copolymer containing core/shell structure disclosed in Japanese Patent Laid Open Publication 6-227124 are desirably used because these compounds display good heat resistance which do not generate sticking by single use at higher temperature than 200xc2x0 C. As concrete examples of commercialized products xe2x80x9cACRYSET SA-532xe2x80x9d (product of NIHON SHOKUBAI Co., Ltd.) and xe2x80x9cMOVINYL 8020xe2x80x9d (product of CLARIANT POLYMER Co., Ltd.) can be mentioned.
Meanwhile, for example, the glass transition temperature (Tg), which is one of the indexes correlating to heat resistance of a fixing agent, of the acrylic ester type copolymer (commercialized name of the product: MOVINYL 35, product of CLARIANT POLYMER Co., Ltd.), a kind of the acrylic ester type resin, is about 25xc2x0 C., and is known to display comparatively good heat resistance. However, since such copolymer does not satisfy the important point of this invention, (namely not becoming sticky at the temperature higher than 200xc2x0 C.), the expected effect can not be obtained from this copolymer.
As the cross-linking agent which can be used in the fixing composition of this invention to prevent the problem of sticking at the temperature higher than 200xc2x0 C., a well-known cross-linking agent can be used as long as it does not deteriorate the thermal recording property and lustrous property. Concretely, dialdehyde type such as glyoxal or polyaldehyde, polyamine type such as polyethylamine, epoxy type, polyamide resin, melamine resin, diglycydil type, dimethylolurea such as glycerindiglycidylether, further, ammonium persulfate, iron chloride and magnesium chloride can be mentioned, however, the invention is not limited to them. Compared with a three-dimensional bridged type glyoxal cross-linking agent, since a two-dimensional bridged type glyoxal does not deteriorate the glossiness, it is useful for the preparation of excellent lustrous surface. The reason why is unclear, however, it is considered that the light scattering is generated on a micro scale when it is three-dimensionally bridged. The amount of cross-linking agent to be added can be adjusted voluntarily so as to be a fixing composition which does not cause sticking at the temperature higher than 200xc2x0 C., and for instance, 0.05-0.3 parts can be added to 1 part of water soluble high polymer substance.
In this invention, good image preservative property can be obtained in addition to the improvement of glossiness by preparing an intermediate layer mainly composed by inorganic pigment and fixing composition. The ground which image preservative property is improved is illustrated as follows. That is, by the presence of an intermediate layer, barrier function, namely, the protecting ability to prevent the penetration of water, plasticizer, oil or solvent into a thermally sensitive recording layer is improved.
As the fixing composition contained in the intermediate layer, any composition which generates barrier function and does not hurt the thermally sensitive recording property and lustrous property can be used. Concretely, various kinds of polyvinyl alcohol of 200xcx9c2500 polymerization degree such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, denatured polyvinyl alcohol, e.g., denatured polyvinyl alcohol by carboxyl, denatured polyvinyl alcohol by amide, denatured polyvinyl alcohol by sulfonic acid or denatured polyvinyl alcohol by butylal, water soluble high polymer of cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and acetyl cellulose and acrylic ester type copolymer resin such as copolymer of (meth)acrylic ester, acrylic ester and/or methacrylic ester, styrene and/or vinyl acetate, copolymer of acrylamide/acrylic ester/methacrylic acid, copolymer of colloidal silica complex acrylic ester and copolymer of colloidal silica complex styrene/acrylic ester can be mentioned. However, it is not intended to be limited to them.
Among above mentioned water soluble high polymer, a highly saponified one or one of high polymerization degree, have a tendency to display high barrier function, and especially a water soluble polymer whose saponification degree is higher than 90% and polymerization degree is higher than 1000. In a case of the intermediate layer, among acrylic ester type resins it is slightly different from the case of glossing layer. In particular, the aforementioned acrylic ester copolymer (commercialized name: MOVINYL 735) is desirably used because it has a good balance of heat resistance and barrier function. Further, when acrylicester resin is contained in the intermediate layer, the glossiness is improved and is desirably used. The reason why is believed to be that the micro smoothness is improved.
Even if a water soluble high polymer can not provide a barrier function to an intermediate layer when used alone, it is possible to improve a barrier function and to use it as a fixing composition in the intermediate layer of this invention by adding a cross-linking agent. As the cross-linking agent which may be used in the fixing composition contained in the intermediate layer of this invention, any kind of well known component which does not hurt the thermally sensitive recording property and the lustrous property can be used. As concrete examples of the cross-linking agent, dialdehyde type, such as, glyoxal or polyaldehyde, polyamine type such as polyethyl amine, epoxy resin, polyamide resin, melamine resin and diglycidyl type dimethylol urea such as glycerin diglycidyl ether, further ammonium persulfate magnesium chloride can be mentioned. However, it is not intended to be limited to them. The amount of the cross-linking agent can be voluntary changed along with the desired property, and the desirable amount is from 0.05-0.35 parts to 1 part of the water soluble high polymer.
Referring to the water soluble polymer such as polyvinyl alcohol used in the glossing layer or the intermediate layer of this invention, the coating viscosity (B type viscometer or high shear type viscometer) becomes high at the preparation of coating, therefore, have a strong point that the coating can be easily coated and high coating amount can be obtained. Therefore, the use of water soluble polymer, such as, polyvinyl alcohol, together with acrylic ester type resin as the fixing composition in the glossing layer or the intermediate layer of this invention is a particularly desirable embodiment. Referring to the lustrous property, since an excellent degree of glossiness can be obtained when the coating amount of glossing layer and intermediate layer is big, small amount of polyvinyl alcohol can be added to provide a coating aptitude, even if other fixing composition is mainly used for the glossing layer or the intermediate layer. In this case, the amount of polyvinyl alcohol to be added is 0.01-0.15 parts to 1 part of fixing composition.
Further, it is effective to add a slipping agent in the glossing layer or the intermediate layer of this invention, for the purpose of improving the thermal head compatibility. As a slipping agent, the slipping agents which are generally used in the conventional thermally sensitive recording medium can be used. As the concrete example, metallic salt of high fatty acid such as zinc stearate or calcium stearate and wax such as paraffin wax, polyethylene wax, carnauba wax, micro crystalline wax and acrylic type wax can be mentioned. Especially, when the thermal head compatibility is concerned, zinc stearate or calcium stearate are desirably used. Further, if the slipping agent is contained in the glossing layer or in the intermediate layer, the phenomenon that the degree of glossiness is improved is observed. The reason for this phenomenon is illustrated as follows. That is, the lustrous property is improved along with the improvement of the surface smoothness.
The inorganic pigment or slipping agent contained in the glossing layer or the intermediate layer, the fixing composition contained in the glossing layer which does not cause sticking at the temperature higher than 200xc2x0 C. and fixing composition contained in the intermediate layer provide an excellent lustrousness when their average particle size is finer than 0.3 xcexcm. Since, this phenomenon is believed to be due to the control of scattering of visible ray by these components, when better glossiness is required, the content of particles bigger than 0.3 xcexcm must be little. Concretely, by limiting the amount of particles bigger than 0.3 xcexcm size to less than 0.03 parts to 1 part of particles smaller than 0.3 xcexcm. Thus, the lustrous degree higher than 70% can be obtained. Especially, in a case of the material which has higher refraction index, the average particle size greatly affects degree of glossiness. So, it is effective to use finer average size to obtain good degree of glossiness. It is more desirable to use fine particles whose average particle size is finer than 0.2 xcexcm to obtain higher degree of glossiness. The particles of these material has an adequate distribution curve, and when the average particle size is finer than 0.2 xcexcm, the size of almost all particles is smaller than the wave length of visible rays.
The kinds and the amount of an inorganic pigment, a fixing composition which does not cause sticking, a slipping agent or other additives contained in the glossing layer of this invention are decided according to the required degree of glossiness are not particularly limited, however, in general, the adequate amount of fixing composition which does not cause sticking at the temperature higher than 200xc2x0 C. is 0.6-3.5 parts desirably 0.75-3.5 parts to 1 part of inorganic pigment, and that of slipping agent is 0.06-1 parts to 1 part of inorganic pigment. Especially, in the case of using paper as a substrate, it is desirable to use 1.0-3.5 parts of fixing composition which does not cause sticking at the temperature higher than 200xc2x0 C. to 1 part of inorganic pigment. On the basis of the total amount of solid contained in the glossing layer, the desirable amount of inorganic pigment and fixing composition which does not cause sticking at the temperature higher than 200xc2x0 C. are respectively 30-60%. Further, by increasing the coating amount to the glossing layer, higher degree of glossiness can be obtained, and ordinary adequate amount is 1-10 g/m2.
When an intermediate layer is prepared between the thermally sensitive recording layer and the glossing layer of this invention, the kinds and the amount of inorganic pigment, fixing composition, slipping agent or other additives contained in the intermediate layer are not limited. However, the desirable amount of inorganic pigment and fixing composition is respectively 30-60% to the total amount of solid contained in the intermediate layer. Further, the amount of coating of the intermediate layer is decided according to the desired image preservative property and degree of glossiness, however, the ordinary adequate amount is 1-4g/m, and if the excellent image preservative property is required the effective coating amount is 2-4g/m2.
The thermally sensitive recording layer of this invention can be prepared by dispersing colorless or pale color dye precursor and organic color developer with binder, adding sensitizer, filler, UV absorbing agent, water proof agent or defoamer as needed and coating and drying the obtained coating over the surface of a substrate.
As a dye precursor used in this invention, all kinds of dye precursors which are well known in the field of pressure sensitive or thermally sensitive recording paper can be used and triphenylmethane type compound, fluorane type compound, fluorene type compound and divinyl type compound are desirably used, however, it is not intended to be limited to them. The concrete examples are shown below. These dye precursors can be used alone or can be used as mixtures of two or more of them.
 less than Triphenylmethane type leuco dyes greater than 
3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide [another name is Crystal Violet Lactone]
3,3-bis(p-dimethylaminophenyl)phthalide [another name is Malachite Green Lactone]
 less than Fluoran type leuco dyes greater than 
3-diethylamino-6-methylfluoran
3-diethylamino-6-methyl-7-anilinofluoran
3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran
3-diethylamino-6-methyl-7-chlorofluoran
3-diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran
3-diethylamino-6-methyl-7-(m-methylanilino)fluoran
3-diethylamino-6-methyl-7-(o-chloroanilino)fluoran
3-diethylamino-6-methyl-7-(p-chloroanilino)fluoran
3-diethylamino-6-methyl-7-(o-fluoroanilino)fluoran
3-diethylamino-6-methyl-7-n-octylanilinofluoran
3-diethylamino-6-methyl-7-n-octylaminonofluoran
3-diethylamino-6-methyl-7-benzylanilinofluoran
3-diethylamino-6-methyl-7-dibenzylanilinofluoran
3-diethylamino-6-chloro-7-methylfluoran
3-diethylamino-6-chloro-7-anilinofluoran
3-diethylamino-6-chloro-7-p-methylanilinofluoran
3-diethylamino-6-ethoxyethyl-7-anilinofluoran
3-diethylamino-7-methylfluoran
3-diethylamino-7-chlorofluoran
3-diethylamino-7-(m-trifluoromethylanilino)fluoran
3-diethylamino-7-(o-chloroanilino)fluoran
3-diethylamino-7-(p-chloroanilino)fluoran
3-diethylamino-7-(o-fluoroanilino)fluoran
3-diethylamino-benzo[a]fluoran
3-diethylamino-benzo[c]fluoran
3-dibutylamino-6-methyl-fluoran
3-dibutylamino-6-methyl-7-anilinofluoran
3-dibutylamino-6-methyl-7-(o,p-dimethylanilino)fluoran
3-dibutylamino-6-methyl-7-(o-chloroanilino)fluoran
3-dibutylamino-6-methyl-7-(p-chloroanilino)fluoran
3-dibutylamino-6-methyl-7-(o-fluoroanilino)fluoran
3-dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran
3-dibutylamino-6-methyl-chlorofluoran
3-dibutylamino-6-ethoxyethyl-7-anilinofluoran
3-dibutylamino-6-chloro-7-anilinofluoran
3-dibutylamino-6-methyl-7-p-methylanilinofluoran
3-dibutylamino-7-(o-chloroanilino)fluoran
3-dibutylamino-7-(o-fluoroanilino)fluoran
3-di-n-pentylamino-6-methyl-7-anilinofluoran
3-di-n-pentylamino-6-methyl-7-(p-chloroanilino)fluoran
3-di-n-pentylamino-7-(m-trifluoromethylanilino)fluoran
3-di-n-pentylamino-6-chloro-7-anilinofluoran
3-di-n-pentylamino-7-(p-chloroanilino)fluoran
3-pyrrolidino-6-methyl-7-anilinofluoran
3-piperidino-6-methyl-7-anilinofluoran
3-(N-methyl-N-n-propylamino)-6-methyl-7-anilinofluoran
3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran
3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran
3-(N-ethyl-N-xylamino)-6-methyl-7-(p-chloroanilino)fluoran
3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran
3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran
3-(N-ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran
3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran
3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran
3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran
3-cyclohexylamino-6-chlorofluoran
2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilinofluoran
2-(4-oxahexyl)-3-diethylamino-6-methyl-7-anilinofluoran
2-(4-oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran
2-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran
2-methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran
2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran
2-chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluoran
2-nitro-6-p-(p-diethylaminophenyl)aminoanilinofluoran
2-amino-6-p-(p-diethylaminophenyl)aminoanilinofluoran
2-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran
2-phenyl-6-metyl-p-(p-phenylaminophenyl)aminoanilinofluoran
2-benzoyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran
2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran
3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran
3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran
3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran
2,4-dimethyl-6-[(4-dimethylamino)anilino]-fluoran
 less than Fluorene type leuco dyes greater than 
3,6,6xe2x80x2-tris(dimethylamino)spiro[fluorene-9,3xe2x80x2-phthalide]
3,6,6xe2x80x2-tris(diethylamino)spiro[fluorene-9,3xe2x80x2-phthalide]
 less than Divinyl type leuco dyes greater than 
3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrabromophthalide
3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrachlorophthalide
3,3-bis-[1,1-bis(4-pyrrolidinophenyl)ethylen-2-yl]-4,5,6,7-tetrabromophthalide 3,3-bis-[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylen-2-yl]-4,5,6,7-tetrachlorophthalide
 less than Others greater than 
3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide
3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide
3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide
3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide
3,6-bis(diethylamino)fluoran-xcex3-(3xe2x80x2-nitro)anilinolactam
3,6-bis(diethylamino)fluoran-xcex3-(4xe2x80x2-nitro)anilinolactam
1,1-bis-[2xe2x80x2,2xe2x80x2,2xe2x80x3,2xe2x80x3-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrilethane
1,1-bis-[2xe2x80x2,2xe2x80x2,2xe2x80x3,2xe2x80x3-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2, -xcex2-naphthoylethane
1,1-bis-[2xe2x80x2,2xe2x80x2,2xe2x80x3,2xe2x80x3-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-diacetylethane bis-[2,2,2xe2x80x2,2xe2x80x2-tetrakis-(p-dimethylaminophenyl)-ethenyl]-methylmalonic acid dimethyl ester.
As examples of organic color developers which may be used in this invention, bisphenol A, 4-hydroxybenzoic acid esters, 4-hydroxyphthalic acid diesters, phthalic acid monoesters, bis-(hydroxyphenyl)sulfides, 4-hydroxyphenylarylsulfones, 4-hydroxyphenylarylsulfonates, 1,3-di[2-(hydroxyphenyl)-2-propyl]-benzenes, 4-hydroxybenzoyloxybenzoic acid esters, derivatives of aminobenzenesulfonamide described in Japanese Patent Laid Open Publication 08-59603, diphenylsulfone cross-linkable type compound described in International Patent Laid Open publication WO97/16420 and bisphenolsulfones described in Japanese Patent Laid Open Publication 03-207688 and Japanese Patent Laid Open Publication 05-24366 can be mentioned. Typical examples of prior color developers are shown below, but it is not intended to be limited to these compounds. These compounds can be used alone or can be used together with each other. Among these compounds, 2,4xe2x80x2-sulfonildiphenyl (another name is 2,4xe2x80x2-bisphenol S) and derivatives of aminobenzenesulfonamide have remarkably good heat resistance, and are suited for the use in which heat resistance is required.
 less than bisphenol A type greater than 
4,4xe2x80x2-isopropylidenediphenol (another name is bisphenol A),
4,4xe2x80x2-cyclohexylidenediphenol,
p,pxe2x80x2-(1 -methyl-n-hexylidene)diphenol,
1,7-di(hydroxyphenylthio)-3,5-dioxaheptane.
 less than 4-hydroxybenzoic acid ester type greater than 
4-hydroxybenzyl benzoate,
4-hydroxyethyl benzoate,
4-hydroxypropyl benzoate,
4-hydroxyisopropyl benzoate,
4-hydroxybutyl benzoate,
4-hydroxyisobutyl benzoate,
4-hydroxymethylbenzyl benzoate.
 less than 4-hydroxyphthalic acid diester type greater than 
4-hydroxydimethylphthalate,
4-hydroxydiisopropylphthalate,
4-hydroxydibenzylphthalate,
4-hydroxydihexylphthalate.
 less than phthalic acid monoester type greater than 
monobenzyl phthalate,
monocyclohexyl phthalate,
monophenyl phthalate,
monomethylphenyl phthalate,
monoethylphenyl phthalate,
monopropylbenzyl phthalate,
monohalogenbenzyl phthalate,
monoethoxybenzyl phthalate.
 less than bis-(hydroxyphenyl)sulfide type greater than 
bis-(4-hydroxy-3-tert-butyl-6-methylphenyl)sulfide,
bis-(4-hydroxy-2,5-dimethylphenyl)sulfide,
bis-(4-hydroxy-2-methyl-5-ethylphenyl)sulfide,
bis-(4-hydroxy-2-methyl-5-isopropylphenyl)sulfide,
bis-(4-hydroxy-2,3-dimethylphenyl)sulfide,
bis-(4-hydroxy-2,5-dimethylphenyl)sulfide,
bis-(4-hydroxy-2,5-diisopropylphenyl)sulfide,
bis-(4-hydroxy-2,3,6-trimethylpheny l)sulfide,
bis-(2,4,5-trihydroxyphenyl)sulfide,
bis-(4-hydroxy-2-cyclohexyl-5-methylphenyl)sulfide,
bis-(2,3,4-trihydroxyphenyl)sulfide,
bis-(4,5-dihydroxy-2-tert-butylphenyl)sulfide,
bis-(4-hydroxy-2,5-diphenylphenyl)sulfide,
bis-(4-hydroxy-2-tert-octyl-5-methylphenyl)sulfide.
 less than 4-hydroxyphenylarylsulfone type greater than 
4-hydroxy-4xe2x80x2-isopropoxydiphenylsulfone,
4-hydroxy-4xe2x80x2-n-propoxydiphenylsulfone,
4-hydroxy-4xe2x80x2-n-butyloxydiphenylsulfone.
 less than 4-hydroxyphenylarylsulfonate type greater than 
4-hydroxyphenylbenzenesulfonate,
4-hydroxyphenyl-p-tolylsulfonate,
4-hydroxyphenylmethylenesulfonate,
4-hydroxyphenyl-p-chlorobenzenesulfonate,
4-hydroxyphenyl-p-tert-butylbenzenesulfonate,
4-hydroxyphenyl-p-isopropoxybenzenesulfonate,
4-hydroxyphenyl-1xe2x80x2-naphthalenesulfonate,
4-hydroxyphenyl-2xe2x80x2-naphthalenesulfonate.
 less than 1,3-di[2-(hydroxyphenyl)-2-propyl]benzene type greater than 
1,3-di[2-(4-hydroxyphenyl)-2-propyl]benzene,
1,3-di[2-(4-hydroxy-3-alkylphenyl)-2-propyl]benzene,
1,3-di[2-(2,4-dihydroxyphenyl)-2-propyl]benzene,
1,3-di[2-(2-hydroxy-5-methylphenyl)-2-propyl]benzene.
 less than resorcinol type greater than 
1,3-dihydroxy-6(xcex1,xcex1-dimethylbenzyl)-benzene.
 less than 4-hydroxybenzoyloxybenzoic acid ester type greater than 
4-hydroxybenzoyloxybenzyl benzoate,
4-hydroxybenzoyloxymethyl benzoate,
4-hydroxybenzoyloxyethyl benzoate,
4-hydroxybenzoyloxypropyl benzoate,
4-hydroxybenzoyloxybutyl benzoate,
4-hydroxybenzoyloxyisopropyl benzoate,
4-hydroxybenzoyloxy-tert-butyl benzoate,
4-hydroxybenzoyloxyhexyl benzoate,
4-hydroxybenzoyloxyoctyl benzoate,
4-hydroxybenzoyloxynonyl benzoate,
4-hydroxybenzoyloxycyclohexyl benzoate,
4-hydroxybenzoyloxyxcex2-phenethyl benzoate,
4-hydroxybenzoyloxyphenyl benzoate,
4-hydroxybenzoyloxyxcex1-naphthyl benzoate,
4-hydroxybenzoyloxyxcex2-naphthyl benzoate,
4-hydroxybenzoyloxy-sec-butyl benzoate
 less than bisphenolsulfone type (I) greater than 
bis-(3-1-butyl-4-hydroxy-6-methylphenyl)sulfone,
bis-(3-ethyl-4-hydroxyphenyl)sulfone,
bis-(3-propyl-4-hydroxyphenyl)sulfone,
bis-(3-methyl-4-hydroxyphenyl)sulfone,
bis-(2-isopropyl-4-hydroxyphenyl)sulfone,
bis-(2-ethyl-4-hydroxyphenyl)sulfone,
bis-(3-chloro-4-hydroxyphenyl)sulfone,
bis-(2,3-dimethyl-4-hydroxyphenyl)sulfone,
bis-(2,5-dimethyl-4-hydroxyphenyl)sulfone,
bis-(3-methoxy-4-hydroxyphenyl)sulfone,
4-hydroxyphenyl-2xe2x80x2-ethyl-4xe2x80x2-hydroxyphenylsulfone,
4-hydroxyphenyl-2xe2x80x2-isopropyl-4xe2x80x2-hydroxyphenylsulfone,
4-hydroxyphenyl-3xe2x80x2-isopropyl-4xe2x80x2-hydroxyphenylsulfone,
4-hydroxyphenyl-3xe2x80x2-sec-butyl-4xe2x80x2-hydroxyphenylsulfone,
3-chloro-4-hydroxyphenyl-3xe2x80x2-isopropyl-4xe2x80x2-hydroxyphenylsulfone,
2-hydroxy-5-t-butylphenyl-4xe2x80x2-hydroxyphenylsulfone,
2-hydroxy-5-t-aminophenyl-4xe2x80x2-hydroxyphenylsulfone,
2-hydroxy-5-t-isopropylphenyl-4xe2x80x2-hydroxyphenylsulfone,
2-hydroxy-5-t-octylphenyl-4xe2x80x2-hydroxyphenylsulfone,
2-hydroxy-5-t-butylphenyl-3xe2x80x2-chloro-4xe2x80x2-hydroxyphenylsulfone,
2-hydroxy-5-t-butylphenyl-3xe2x80x2-methyl-4xe2x80x2-hydroxyphenylsulfone,
2-hydroxy-5-t-butylphenyl-3xe2x80x2-isopropyl-4xe2x80x2-hydroxyphenylsulfone,
2-hydroxy-5-t-butylphenyl-2xe2x80x2-methyl-4xe2x80x2-hydroxyphenylsulfone.
 less than bisphenolsulfone type (II) greater than 
4,4xe2x80x2-sulfonyldiphenol,
2,4xe2x80x2-sulfonyidiphenol,
3,3xe2x80x2-dichloro-4,4xe2x80x2-sulfonyidiphenol,
3,3xe2x80x2-dibromo-4,4xe2x80x2-sulfonyidiphenol,
3,3xe2x80x2,5,5xe2x80x2-tetrabromo-4,4xe2x80x2-sulfonyidiphenol,
3,3xe2x80x2-diamino-4,4xe2x80x2-sulfonyIdiphenol.
 less than others greater than 
p-tert-butylphenol,
2,4-dihydroxybenzophenone,
novolac type phenolic resin,
4-hydroxyacetophenone,
p-phenylphenol,
benzyl-4-hydroxyphenylacetate,
p-benzylphenol.
4,4xe2x80x2-bis(p-tolylsulfonylaminocarbonilamino)diphenylmethane,
4,4xe2x80x2-bis(phenylaminotiocarbonylamino)diphenylsufido.
Further, metallic chelate type color developing components composed by higher fatty acid metal double salt and polyhydric hydroxy.aromatic compound disclosed in Japanese Patent Laid Open Publication 10-258577 or others can be used as the image forming material. And, these chelate type color developing components can be used alone or can be used together with afore mentioned leuco dye and organic color developer.
In this invention, a conventional well known sensitizer can be used with the limitation that the desired effect of this invention is not prevented. As examples of the sensitizer,
stearic acid amide,
palmitic acid amide,
methoxycarbonyl-N-benzamidestearate,
N-benzoyl stearic acid amide,
N-eicosenoic acid amide,
ethylene-bis-stearic acid amide,
behenic acid amide,
methylene-bis-stearic acid amide,
methylolamide,
N-methylolsteric acid amide,
dibenzyl terephthalate,
dimethyl terephthalate,
dioctyl terephthalate,
p-benzyloxybenzylbenzoate,
1-hydroxy-2-phenylnaphthoate,
dibenzyloxalate
di-p-methylbenzyloxalate,
di-p-chlorobenzyloxalate,
2-naphthylbenzylether,
m-terphenyl,
p-benzylbiphenyl,
4-biphenyl-p-tolylether
di(p-methoxyphenoxyethyl)ether
1,2-di(3-methylphenoxy)ethane
1,2-di(4-methylphenoxy)ethane
1,2-di(4-methoxyphenoxy)ethane
1,2-di(4-chlorophenoxy)ethane
1,2-diphenoxyethane
1-(4-methoxyphenoxy)-2-(2-methylphenoxy)ethane
p-methyltiophenylbenzylether
1,4-di(phenyltio)buthane
p-acetotoluidide
p-acetophenetidide,
N-acetoacetyl-p-toluidine,
di-(xcex2-biphenylethoxy)benzene,
p-di(vinyloxyethoxy)benzene,
1-isopropylphenyl-2-phenylethane
1,2-bis(phenoxymethyl)benzene
p-toluenesulfonamide,
o-toluenesulfonamide,
di-p-tolylcarbonate and
phenyl-xcex1-naphtylcarbonate
can be mentioned, however it is not intended to be limited to these compounds. These sensitizers can be used alone or by mixing more than two kinds of them.
As the binder used in the present invention, various kinds of polyvinyl alcohol of 200xcx9c2500 polymerization degree such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, denatured polyvinyl alcohol (e.g. denatured polyvinyl alcohol by carboxyl, denatured polyvinyl alcohol by amide, denatured polyvinyl alcohol by sulfonic acid or denatured polyvinyl alcohol by butylal), derivatives of cellulose such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and acetyl cellulose, copolymer of styrene-maleic anhydride, copolymer of styrene-butadiene, polyvinyl chloride, polyvinyl acetal, polyacrylicamide, polyacrylic acid ester, polyvinylbutyral, polystyrene or copolymer of them,polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin and cumarone resin can be mentioned. These macro molecule compounds can be applied by being dissolved into solvents such as water, alcohol, ketone, ester or hydrocarbon or by being dispersed in water or other medium under an emulsion state or a paste state and these forms of application can be used in combination according to the quality requirement.
As a filler which can be used in this invention, an inorganic or an organic filler such as silica, calcium carbonate, kaoline, calcined kaoline, diatomaceous earth, talc, titanium oxide, zinc oxide, aluminum hydroxide, polystyrene resin, urea-formaldehyde resin, copolymer of styrene-methacrylic acid, copolymer of styrene-butadiene and hollow plastic pigment can be mentioned.
Further, a parting agent such as metallic salt of fatty acid, a slipping agent such as wax, benzophenon- or triazole-based ultraviolet absorbers, water proof agent such as glyoxal, dispersing agent, defoamers, anti-oxidation agent and fluorescent dye can be used as an additive.
As a substrate, paper, synthetic paper, plastic film, plastic foam film, non-woven fabric, recycled paper metallic foil and a complex of these materials can be used.
The amount of color developer and dye precursor, the kind and amount of other additives to be used in the thermally sensitive recording medium of this invention are decided according to the required quality and recording feature, and are not particularly restricted. However, in general, it is preferable to use 0.1-2 parts of dye precursor, 0.5xcx9c4 parts of filler and 0.05-2 parts of stabilizer and sensitizer to 1 part of color developer and 5xcx9c25% of binder to the total amount of solid.
The color developer, dye and other additives which are added at need are ground to fine particles smaller than several microns diameter by means of a pulverizer such as a ball mill, an attriter or a sand grinder, or by means of an adequate emulsifying apparatus, then binder and other additives are added at need, thus the coating is prepared. As a method to coat the coating, a hand coating, a size press coating method, a roll coating method, an air knife coating method, a blend coating method, a flow coating method, a comma direct method, a gravure direct method, a gravure reverse method and a reverse roll coating method can be mentioned. Further, the method to dry up after sputtering, spraying or dipping can also be used.
In the thermally sensitive recording medium of this invention, an undercoating layer composed mainly by filler and binder can be formed between thermally sensitive recording layer and substrate for the purpose to improve the quality of image. As the binder, the filler and other additives contained in the undercoating layer, the materials which are indicated as the compound composing the thermally sensitive recording layer can be used according to the required quality. Among these compounds, calcined kaolin, fine hollow spherical particle with shell disclosed in Japanese Patent Publication 3-54074 or cup shape hollow polymer particle disclosed in Japanese Patent Laid Open Publication 10-258577 can be desirably used, because these fillers used to the undercoating layer of the conventional thermally sensitive recording medium has a good function as a heat insulating material. Further, the resistance to water or to chemicals of the recorded image or ground part against the water or chemicals which may bleed out from the back surface of substrate can be improved by containing well known cross-linking agent such as glyoxal.
In the thermally sensitive recording medium of this invention, a back coating layer can be formed under the back surface of the substrate to prevent the bleeding out of water or chemicals from the back surface of the substrate. In this case, it is desirable to use above mentioned binder and cross-linking agent such as glyoxal.
The thermally sensitive recording medium of this invention can be applied to various fields of use. Especially, because of the above mentioned excellent glossiness and image preservative property, it is applied to a thermally sensitive label sheet or a thermally sensitive recording type magnetic ticket paper. In a case of thermally sensitive label, a thermally sensitive recording layer, a glossing layer and an intermediate layer at need are formed on one side of the substrate, and a release paper (liner) is provided on another side of the substrate through an adhesive layer or a sticking agent layer. And in a magnetic ticket paper, a magnetic recording layer mainly composed by strong magnetic substance and fixing agent is formed instead of release paper.
The thermally sensitive recording medium of this invention can obtain an excellent luster without a calendar treatment. If higher degree of glossiness (angle of incidence and angle of reflect is 75xc2x0) is required, it is effective to make the surface smoothness higher than 3000 second by Beck Smoothness by a calendar treatment. Thus, by improving surface smoothness of the thermally sensitive recording medium, since the scattering of rays at the surface is controlled, it is effective to obtain higher degree of glossiness. Especially, if degree of glossiness higher than 80% is required, it is desirable to make the smoothness higher than 5000 second.